Pressure-sensitive indicating switch

ABSTRACT

A pressure-sensitive indicating switch comprises an electroluminescent lamp assembly having a pressure-sensitive variable resistance layer interposed between the phosphor and one conductor thereof. Depression of the switch compresses the pressure-sensitive layer, reducing its resistance and allowing current flow through the phosphor thereby illuminating the lamp. Additional provisions include an optical feedback means and means for remotely activating the lamp assembly.

United States Patent [72] Inventor Alfred J. Maclntyre Nashua, NH.

[21 Appl. No. 884,530

[22] Filed Dec. 12, 1969 [45] Patented Dec. 7, 1971 [73] Assignee Sanders Associates, Inc.

Nashua, N.H.

[54] PRESSURE-SENSITIVE INDICATING SWITCH 14 Claims, 4 Drawing Figs.

[52] 1.1.8. Cl 315/149, 313/108, 315/159 [51] Int. Cl H05b 37/02 [50] Field of Search 313/108,

[56] References Cited UNITED STATES PATENTS 2,816,236 12/1957 Rosen 315/55 X 2,951,817 9/1960 Myers. 338/47 X 3,358,185 12/1967 Lally 315/169 X 3,379,927 4/1968 Yando 315/55 Primary Examiner Roy Lake Assistant Examiner-Lawrence .l. Dahl Attorney-Louis Etlinger PRESSURE-SENSITIVE INDICATIING SWIITQII BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to the field of electrical switching apparatus and more particularly to pressuresensitive switches having an electroluminescent indicating element as an integral part thereof.

2. Description of the Prior Art Prior to the present invention the field of pressure-sensitive indicating switches was typified by assemblies using mechanical switch contacts and a filament bulb in series with the contacts. A number of problems attend the use of such switches including the difficulty presented in sealing mechanical switch contacts against humidity and the catastrophic failure mode of lamp filaments as well as their relatively high current consumption and heat generation characteristics.

Objects and Summary of the Invention It is therefore a primary object of the present invention to provide a new and novel pressure-sensitive indicating switch.

It is another objective of the present invention to provide apparatus of the above-described character having no mechanical switch contacts.

It is an additional object of the present invention to provide apparatus of the above-described character which is not subject to catastrophic failure.

It is a further object of the present invention to provide apparatus of the above-described character having an optical latch to maintain switch illumination after removal of pressure.

It is also an object of the present invention to provide apparatus of the above-described character including means for remotely activating the switch indicating means.

The foregoing and other objectives of the present invention are achieved by providing an electroluminescent lamp assembly having a pressure-sensitive variable resistance layer in terposed between the phosphor and one conductor of the assembly. Depression of the switch compresses the variable resistance layer thus permitting current to flow through the phosphor layer thereby illuminating the lamp. In one embodiment a second pressure-sensitive variable resistance layer is disposed between conductive layers and the assembly is disposed adjacent a pressure-sensitive electroluminescent indicating assembly. Depression of the switch compresses both variable resistance layers thereby closing an electrical circuit coupled across the second variable resistance and activating the electroluminescent phosphor. A photoconductive optical feedback feature may be used to provide switch illumination which persists for a period of time after pressure is removed from the switch. In a further embodiment of the invention a transducer activated by closure of an external circuit may be provided whereby the pressure-sensitive electroluminescent lamp assembly is activated.

These and other objects, features and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. l is a schematic cross section view of a pressure-sensitive indicator constructed in accordance with the principles of the present invention.

FIG. 2 is a schematic cross section view of a pressure-sensitive indicating switch in accordance with the present invention.

FIG. 3 is a schematic cross section view of a pressure-sensitive switch indicator having an optical feedback means.

FIG. 4 is a schematic cross section view of a pressure-sensitive indicator having means for remotely applying activating pressure thereto.

DESCRIPTION UF PREFERRED EMBODIMENTS With reference now to FIG. ii there is schematically illustrated in cross section a pressure-sensitive indicator in accordance with the present invention. A layer of pressure-sensitive variable resistance material lltl is disposed between a layer of electroluminescent phosphor I2 and a rigid substrate conductor MI. The other electrically conductive layer I6 essential to the electroluminescent lamp assembly is formed of an optically transmissive and preferably flexible material such as metallized mylar. The flexible conductor I6 may then be covered with an optically transmissive, flexible layer of insulation 118-. The pressure-sensitive variable resistance layer It) may comprise a pressure cell made from the rare earths processed with zirconium tetra-chloride as described by Dudley 13. Clark in an article entitled Pressure-Sensitive Material Measures Explosion Forces...or Footfall of a Fly" appearing in the Sept. 16, I957 issue of Product Engineering. In the alternative a variable resistance material formed of pliable polyvinyl chloride with a conductive filler as described in US. Pat. No. 2,95l,817 which issued to T. E. Myers on Sept. 6, 1960 may also be of utility in the practice of the present invention. In either case the effect of the Pressure-sensitive variable resistance layer ill) is to prevent current flow through the electroluminescent phosphor when no pressure is applied to the flexible front surface M of the cell. W hen pressure is applied to surface 18 the flexible conductor I6 and phosphor layer I2 are deformed such that the pressuresensitive variable resistance layer III is compressed. This compression lowers the electrical resistance of the layer III and current from the AC source 2 3 flows from the rigid conductor 114, through the pressure-sensitive layer III and the phosphor layer I2 to the flexible conductor 16 thereby causing the emission of light from the phosphor layer I2 and illuminating the switch. Removing pressure from the surface III, due to the resiliency of the pressure-sensitive material III, raises the resistance of layer III thus causing a voltage drop sulficient to prevent the emission of light from the phosphor layer 112. It will be understood that a particular application of the invention may require the use of an additional light reflecting layer between the phosphor and pressure-sensitive layers to enhance the switch illumination in accordance with known electroluminescent fabrication techniques. Being known to those skilled in the art such reflecting layer is not illustrated for the purposes of clarity.

A pressure-sensitive indicating switch according to the present invention is schematically illustrated in the cross section view of FIG. 2. This embodiment comprises a pressuresensitive indicating element 22 which is of the same construction and operation as the apparatus shown in FIG. I and wherein like elements are identified by like numerals and a switching element 24. The switching element 2 includes a second layer 26 of pressure-sensitive variable resistance material of the character described above which is disposed between electrically conductive layers 28 and 36. An external circuit, schematically shown for illustrative purposes only as a power supply 32 and a utilization means 34, is coupled across the conductive layers 2% and MI. The indicating element 22 and switching element 24 are electrically isolated from one another by a layer of insulation 36 of any suitable type. In practice the indicating and switching elements 22 and 24 together with the insulating layer 36 may be laminated together to form the complete pressure-sensitive indicating switch. In operation when pressure is applied to the front surface I of the indicating element both layers of pressure-sensitive variable resistance material III and 26 are compressed, and the respective resistances thereof are lowered permitting current to flow therethrough. The current flow from AC source through the indicating element 22 causes emission of light from the electroluminescent phosphor layer I2 thereby illuminating the switch face. The lowering of the electrical resistance of layer 26 operates to close the external circuit and permit current flow from the power supply 352 through the utilization means 31 i.

FIG. 3 is a schematic cross section view of an embodiment of the present invention wherein an optical feedback feature is provided. In this embodiment an optically transparent electrically conductive layer 38 is interposed between a layer of electroluminescent phosphor 40 and an annular layer of pressuresensitive variable resistance material 42. A photoconductive element 44 is disposed through the pressure-sensitive layer 42 such that it is in electrical contact with the transparent conductor 38 and the rear substrate conductor 46. The front conductor 48 is both flexible and optically transparent as discussed hereinabove and may have a layer of insulation 50 disposed over the front surface thereof. When pressure is applied to the front surface 50 of the indicator the electrical resistance of the pressure-sensitive material 42 is lowered in the above-described manner and current flows from the AC source 52 through the substrate conductor 46, pressure-sensitive resistance 42, transparent conductor 38, electroluminescent phosphor 40 and front conductor 48 and light is emitted by the phosphor 40. Some of the light from the phosphor 40 is fed back through the transparent conductive layer 38 to the surface of the photoconductive element 44 thereby lowering the electrical resistance thereof. Thus when pressure is removed from the front surface 50 of the indicator of FIG. 3 the resistance decay characteristic of the photoconductiveelement 44 continues to permit current flow through the phosphor layer 40 and once activated the indicator remains illuminated. It will be apparent that the indicator of FIG. 3 is directly applicable to use in combination with the switching element discussed hereinabove with reference to FIG. 2.

Turning now to FIG. 4 there is schematically illustrated in cross section a pressure-activated switch indicator in accordance with the present invention. The indicating element 53 comprises a flexible conductive layer 54, a layer of pressure-sensitive variable resistance material 56, a layer of electroluminescent phosphor 58 and an optically transparent front conductor 60 which may be provided with a layer 62 of insulating material. The activating element 64 comprises a transducer layer 66 formed of one of a class of ceramic materials typified by barium titanate. These materials inhibit the piezoelectric effect and enhance the electrostrictive effect; thus when laminated between first and second flexible conductive layers 68 and 70 across which an electric field is applied, the transducer deforms in a cupping action. The transducer 66 together with its flexible conductive layers 68 and 70 is electrically isolated from the indicating element 53 by a layer of insulation 69 and is placed in an external electrical circuit herein illustrated merely as a power supply 72, utilization means 73 and switch 74. When switch 74 is closed an electric field is applied across the transducer 66 and the activating element 64 deforms in a cupping action thus applying pressure to the flexible conductor 54 and pressure-sensitive variable resistance layer 56. Compression of the pressure-sen sitive layer 56 causes a reduction in the electrical resistance thereof and current flows from the AC source 76 activating the electroluminescent phosphor 58 in the above-described manner. Thus the present invention provides a pressure-sensitive electroluminescent indicator which is activated by a remote switch. It will be apparent that the optical feedback feature illustrated in FIG. 3 may further be incorporated in the embodiment of FIG. 4 and thereby provide a latching-type indicator.

It will be apparent from the foregoing description that the objectives of the present invention have been efficiently met and since certain changes in the above-described construction will become apparent to those skilled in the art it is intended that all matter contained in the foregoing description or shown in the appended drawings shall be interpreted as illustrative rather than in a limiting sense.

Having described what is new and novel and desired to secure by Letters Patent, what is claimed is:

l. A pressure-sensitive indicating switch comprising:

a layer of electroluminescent phosphor material,

a layer of optically transmissive electrically conductive material disposed in electrical contact with said phosphor layer,

a layer of pressure-sensitive variable resistance material disposed in electrical contact with said phosphor layer opposite said optically transmissive conductive layer,

an electrically conductive substrate layer disposed in electrical contact with said pressure-sensitive variable resistance layer opposite said phosphor layer, and

a source of electrical power coupled between said optically transmissive and substrate conductive layers whereby pressure applied to said optically transmissive conductive layer produces compression of said pressure-sensitive variable resistance material reducing the resistance thereof and causing current from said source to flow through the assembly activating said phosphor material.

2. Apparatus as recited in claim 1 wherein:

said pressure-sensitive variable resistance material is formed of a rare earth treated with zirconium tetrachloride.

3. Apparatus as recited in claim I wherein:

said pressure-sensitive variable resistance material is formed of pliable polyvinyl chloride having an electrically conductive filler distributed therein.

4. Apparatus as recited in claim 1 wherein:

said optically transmissive layer is formed of a flexible electrically conductive material.

5. Apparatus as recited in claim 4 wherein:

said flexible optically transmissive conductive material is metallized mylar.

6. Apparatus as recited in claim 1 further including:

a layer of optically transmissive electrical insulation disposed on the surface of said optically transmissive conductive layer opposite said phosphor layer.

7. Apparatus as recited in claim 1 further including:

a second optically transmissive electrically conductive layer disposed between said phosphor layer and said pressuresensitive variable resistance layer, and

a photoconductive element disposed through said pressuresensitive variable resistance layer in electrical contact with said substrate conductive layer and said second optically transmissive conductive layer whereby optical feedback is provided such that phosphor material remains activated subsequent to removal of pressure from said switch.

8. Apparatus as recited in claim I further including: a

second layer of pressure-sensitive variable resistance material,

first and second layers of electrically conductive material disposed in electrical contact with opposed surfaces of said second pressure-sensitive layer,

a layer of electrical insulation disposed between one of said first and second conductive layers and said substrate conductive layer, and

an external circuit coupled across said first and second conductive layers whereby pressure applied to said optically transmissive conductive layer produces compression of said first and second pressuresensitive variable resistance layers thereby activating said phosphor material and said external circuit.

9. A'pressure-activated switch indicator comprising:

a transducer layer which undergoes predetermined deformation under the influence of an electrical field,

first and second flexible electrically conductive layers disposed in electrical contact with opposed surfaces of said transducer layer,

a selectively activated external electrical circuit coupled between said first and second conductive layers,

a layer of electrical insulation disposed adjacent one of said first and second conductive layers opposite said transducer layer,

a third electrically conductive layer disposed adjacent said insulation layer,

a layer of pressure-sensitive variable resistance material disposed in electrical contact with said third conductive layer opposite said insulation layer,

a layer of electroluminescent phosphor material disposed in electrical contact with said pressure-sensitive layer opposite said third conductive layer,

an optically transmissive electrically conductive layer disposed in electrical contact with said phosphor layer opposite said pressure-sensitive layer, and

a source of electrical power coupled between said optically transmissive and third conductive layers whereby activation of said external circuit produces an electric field across said transducer causing deformation thereof such as to apply pressure to said pressure-sensitive variable resistance layer thereby activating said phosphor material.

10. Apparatus as recited in claim 9 further including:

a second optically transmissive electrically conductive layer disposed between said phosphor layer and said pressuresensitive variable resistance layer, and

a photoconductive element disposed through said pressuresensitive variable resistance layer in electrical contact with said third conductive layer and said second optically transmissive conductive layer whereby optical feedback is provided such that said phosphor material remains activated subsequent to deactivation of said external circuit.

ll ll. Apparatus as recited in claim 9 wherein:

said pressure-sensitive variable resistance material is formed of a rare earth treated with zirconium tetrachloride.

ll2. Apparatus as recited in claim 9 wherein:

said pressure-sensitive variable resistance layer is formed of pliable polyvinyl chloride having an electrically conductive filler distributed therein.

13. Apparatus as recited in claim 9 wherein:

said transducer is formed of a ceramic material which inhibits the piezoelectric effect and enhances the electros trictive effect under the influence of an electric field.

M. Apparatus as recited in claim 13 wherein:

said transducer is formed of barium titanate. 

1. A pressure-sensitive indicating switch comprising: a layer of electroluminescent phosphor material, a layer of optically transmissive electrically conductive material disposed in electrical contact with said phosphor layer, a layer of pressure-sensitive variable resistance material disposed in electrical contact with said phosphor layer opposite said optically transmissive conductive layer, an electrically conductive substrate layer disposed in electrical contact with said pressure-sensitive variable resistance layer opposite said phosphor layer, and a source of electrical power coupled between said optically transmissive and substrate conductive layers whereby pressure applied to said optically transmissive conductive layer produces compression of said pressure-sensitive variable resistance material reducing the resistance thereof and causing current from said source to flow through the assembly activating said phosphor material.
 2. Apparatus as recited in claim 1 wherein: said pressure-sensitive variable resistance material is formed of a rare earth treated with zirconium tetra-chloride.
 3. Apparatus as recited in claim 1 wherein: said pressure-sensitive variable resistance material is formed of pliable polyvinyl chloride having an electrically conductive filler distributed therein.
 4. Apparatus as recited in claim 1 wherein: said optically transmissive layer is formed of a flexible electrically conductive material.
 5. Apparatus as recited in claim 4 wherein: said flexible optically transmissive conductive material is metallized mylar.
 6. Apparatus as recited in claim 1 further including: a layer of optically transmissive electrical insulation disposed on the surface of said optically transmissive conductive layer opposite said phosphor layer.
 7. Apparatus as recited in claim 1 further including: a second optically transmissive electrically conductive layer disposed between said phosphor layer and said pressure-sensitive variable resistance layer, and a photoconductive element disposed through said pressure-sensitive variable resistance layer in electrical contact with said substrate conductive layer and said second optically transmissive conductive layer whereby optical feedback is provided such that said phosphor material remains activated subsequent to removal of pressure from said switch.
 8. Apparatus as recited in claim 1 further including: a second layer of pressure-sensitive variable resistance material, first and second layers of electrically conductive material disposed in electrical contact with opposed surfaces of said second pressure-sensitive layer, a layer of electrical insulation disposed between one of said first and second conductive layers and said substrate conductive layer, and an external circuit coupled across said first and second conductive layers whereby pressure applied to said optically transmissive conductive layer produces compression of said first and second pressure-sensitive variable resistance layers thereby activating said phosphor material and said external circuit.
 9. A pressure-activated switch indicator comprising: a transducer layer which undergoes predetermined deformation under the influence of an electrical field, first and second flexible electrically conductive layers disposed in electrical contact with opposed surfaces of said transducer layer, a selectively activated external electrical circuit coupled between said first and second conductive layers, a layer of electrical insulation disposed adjacent one of said first and second conductive layers opposite said transducer layer, a third electrically conductive layer disposed adjacent said insulation layer, a layer of pressure-sensitive variable resistance material disposed in electrical contact with said third conductive layer opposite said insulation layer, a layer of electroluminescent phosphor material disposed in electrical contact with said pressure-sensitive layer opposite said third conductive layer, an optically transmissive electrically conductive layer disposed in electrical contact with said phosphor layer opposite said pressure-sensitive layer, and a source of electrical power coupled between said optically transmissive and third conductive layers whereby activation of said external circuit produces an electric field across said transducer causing deformation thereof such as to apply pressure to said pressure-sensitive variable resistance layer thereby activating said phosphor material.
 10. Apparatus as recited in claim 9 further including: a second optically transmissive electrically conductive layer disposed between said phosphor layer and said pressure-sensitive variable resistance layer, and a photoconductive element disposed through said pressure-sensitive variable resistance layer in electrical contact with said third conductive layer and said second optically transmissive conductive layer whereby optical feedback is provided such that said phosphor material remains activated subsequent to deactivation of said external circuit.
 11. Apparatus as recited in claim 9 wherein: said pressure-sensitive variable resistance material is formed of a rare earth treated with zirconium tetra-chloride.
 12. Apparatus as recited in claim 9 wherein: said pressure-sensitive variable resistance layer is formed of pliable polyvinyl chloride having an electrically conductive filler distributed therein.
 13. Apparatus as recited in claim 9 wherein: said transducer is formed of a ceramic material which inhibits the piezoelectric effect and enhances the electrostrictive effect under the influence of an electric field.
 14. Apparatus as recited in claim 13 wherein: said transducer is formed of barium titanate. 